3-(2-Hydroxybenzoyloxy)-4-(trimethylammonio)butyrobetaine hydrochloride, as the ester of salicylic acid with carnitine (salicyloyl carnitine), is a salicylic acid derivative with very promising therapeutic properties (EP 553385). The only known process for preparing salicyloyl carnitine starts with L-carnitine HCl and the acid chloride of salicylic acid, whose hydroxy group is protected by a methyl group. This methyl group can be cleaved only by use of highly concentrated hydrobromic acid. The yield from this cleavage is moderate (50%). In addition, the hydrobromide of salicyloyl carnitine is formed, which for pharmaceutical use must be converted either to free betaine or its hydrochloride, using an ion exchange resin. Over all stages, the yield of salicyloyl carnitine hydrochloride is only 35%.
Therefore, it is an object of the present invention to provide an improved process for preparing 3-(2-hydroxybenzoyloxy)-4-(trimethylammonio)butyrobetaine hydrochloride. In particular, it is an object of the present invention to provide a short and thus cost-effective process, preferably with high yield, for preparing 3-(2-hydroxybenzoyloxy)-4-(trimethylammonio)butyrobetaine hydrochloride.